lost spark

[smbikes1867]

After doing a topend rebuild on my 1988 yz 250 and 1 good day of riding and braking it in , i left the gas on and it flooded the bike baddd. i hade to take the redvavle, fatty pipe and every thing els off so it could dry out. the i put it back together and it seem to have a bog and did not pick up power , so the next day i changed the plug and took it for a ride , it seem to have a little pop in the exhaust, then as i went up a hill and it cut off. when i got home i put a new plug in agane and it had no spark , i put in a new coil and it still has no spark :bang: Im pulling the flywheel to day, Any ides what it could be?? Or what to check.

 

[Uchytil]

The first thing to check is the stop circuit. It's a wire that grounds the charge side of the CDI. Disconnect the stop switch wire and see if you have spark. Try to disconnect it as close to the CDI as possible. Also check all of your ground connections! Yamaha mostly uses grounds to complete circuits if one is loose or worse disconnected your problem is solved. For me to do a proper spark test I use a spark tester to check the secondary (plug wire) loaded V test. If you have the correct HR plug and it's new that should suffice, just ground it (don't hold on though - ouch). The coil you changed, did it have a new boot? Sometimes it as simple as the boot and you would know when you do the resistance on the sec side. Did you check the old coil? I don't have the specs but the primary side would be low. say an ohm and the secondary might be about 3-4K ohms (unless the cap is a resistance cap and then you would add about 4K ohms).. You can test the CDI for peak voltage and you need a tester. You can check input/output and that's all on the CDI.